80 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



number of holes, from three to seven decimetres across, eaten straight 

 down into the body of the I'ock. This peculiar form of etching or decay 

 has been seen on no other stone reef. 



The bedding is plainly visible, and several observations show that the 

 dip is seaward at an angle of from seven to nine degrees. 



Here and there along the outer edge, the reef has been more or less 

 undermined, and great blocks of stone have been detached and their 

 outer edges have sunk. 



The surface of the reef is unusually rough, ragged, and etched, and 

 many loose blocks lie over the top. The rock is very hard and quartz- 

 itic in fracture, and rings when struck with the hammer. 



Eight hundred metres south of its northern end, there is a break in this 

 reef through which the sea has been able to cut out one of the beautiful 

 little semi-lunar bays mentioned and described elsewhere in this paper. 



The Serinhaem reef is a straight one lying between the shore and the 

 island of Santo Aleixo. Its total length is between three and four 

 kilometres, and its bearing north 50° east, magnetic. The south end 

 of the reef is about half a kilometre south of the mouth of Eio Serin- 

 haem, while the north end projects boldly across the embayment south 

 of Ponta do Serramby. The north end is broken, and its extreme point 

 in that direction is represented only by sunken rocks. Near its middle, 

 and opposite the river's mouth and a little south of it, this reef is a 

 double one ; or, if the Cacimba reef be considered, they may all be 

 looked upon as a treble reef. Of this group the Serinhaem is the outer 

 one, the Cacimba reef is the landward one, while a third reef lies about 

 halfway between them. 



This middle reef is more or less fragmentary, yet clearly defined both 

 in its position and its direction. It is parallel with the reefs on both 

 sides of it. 



It was noted the last time these reefs were visited (July 26, 1899), 

 that the muddy waters of the Eio Serinhaem were discharging to the 

 southward and not northward, as do most of the streams along this part 

 of the coast. 



The stone reef of Santo Aleixo. — Santo Aleixo is a small island oppo- 

 site the Barra de Serinhaem, and about two and a half kilometres from 

 the main land. It is also known to navigators as Donally's Island. It 

 is eight hundred and eighty-thi-ee metres long, its longest axis being 

 north-south. The body of the island is of quartz porphyry/ which on 



1 In his Espace Celeste, p. 548, Liais says the rocks of Santo Aleixo are eurities 

 and diorities ; in his Climats Geologic, etc., he says they are amphibole and mag- 



